Conglomerate, Racemate, and Achiral Crystals of Polymetallic Europium(III) Compounds of Bis- or Tris-ß-diketonate Ligands and Circularly Polarized Luminescence Study.

This work reports (a) conglomerate and racemic crystal structures of [(Δ,Δ,Δ,Δ,Δ,Δ)- or/and (Λ,Λ,Λ,Λ,Λ,Λ)-EuIII 6(TTP)8(OH2)6Na4] n coordination polymers, (b) racemic crystal structures of (Δ,Δ,Δ,Δ)-/(Λ,Λ,Λ,Λ)-EuIII 4(TTP)4(bipy)4(MEK)2(OH2)2 tetrahedral clusters, and (c) the achiral crystal structure of the [EuIII 2(BTP)4(OH2)2Na2] n coordination polymer (where BTP = dianionic bis-ß-diketonate, TTP = trianionic tris-ß-diketonate, and bipy = 2,2'-bipyridine). The screw coordination arrangement of the TTP ligand has led to the formation of homoconfigurational racemic EuIII products. The conglomerate crystallization of [EuIII 6(TTP)8(OH2)6Na4] n appears to be caused by the presence of the sodium, Na+ counterions, and interactions between oxygen atoms and the trifluoromethyl unit of the TTP ligand and Na+ ions. All the EuIII compounds exhibit characteristic red luminescence (5D0 → 7FJ, J = 0-4) in solution or in the solid crystalline state. Circularly polarized luminescence (CPL) was observed in the chiral EuIII 6(TTP)8(OH2)6Na4] n species, displaying a |g lum| value in the range of 0.15 to 0.68 at the 5D0 → 7F1 emission band. Subtle changes of the [EuIII 6(TTP)8(OH2)6Na4] n structure which may be due to selection of twinned crystals or crystals that do not correspond to a perfect spontaneous resolution, are considered to be responsible for the variation in the observed CPL values.

Tetrathienyl Corannulene Compounds with Highly Sensitive Photochromism.

We have designed and synthesized photochromic tetrathienyl corannulene compounds, 1,2,7,8-tetrakis(2-methyl-5-phenylthiophen-3-yl)corannulene (1) and 1,2,7,8-tetrakis(2,4-dimethyl-5-phenylthiophen-3-yl)corannulene (2), by fusing two units of photochromic terarylene with a curved aromatic corannulene with a promising antenna effect. Compound 1 exhibited highly sensitive photoreactivity, with a large molar absorption coefficient of 8.2×104  M-1 cm-1 and practically photon-quantitative photocyclization. On the other hand, a terarylene derivative with a planar aromatic phenanthrene, 9,10-bis(2,4-dimethyl-5-phenylthiophen-3-yl)phenanthrene (4) showed no photoreactivity. The reason for such a difference was attributed to the predominance of the photoreactive atropisomers amplified by energy migration, and the shortened distance between reactive carbons induced by the curved structure.

Molecular Rotor Functionalized with a Photoresponsive Brake.

A molecular motor that has been previously shown to rotate when fueled by electrons through a scanning tunneling microscope tip has been functionalized with a terarylene photochrome fragment on its rotating subunit. Photoisomerization has been performed under UV irradiation. Variable-temperature 1H NMR and UV-vis studies demonstrate the rotational motion and its braking action after photoisomerization. The braking action can be reversed by thermal heating. Once the rigid and planar closed form is obtained, the rotation is effectively slowed at lower temperature, making this new rotor a potential motor with an independent response to electrons and light.

Corrigendum: Chirogenesis and Pfeiffer Effect in Optically Inactive EuIII and TbIII Tris(ß-diketonate) Upon Intermolecular Chirality Transfer From Poly- and Monosaccharide Alkyl Esters and α-Pinene: Emerging Circularly Polarized Luminescence (CPL) and Circular Dichroism (CD).

[This corrects the article DOI: 10.3389/fchem.2020.00685.].

Visible Circularly Polarized Luminescence of Octanuclear Circular Eu(III) Helicate.

This work reports on the structural and photophysical characterization of D4-symmetrical octanuclear circular LnIII helicates, [(R)- or (S)-iPr-Pybox]8(LnIII)8(THP)8 (where Ln = Eu and Tb, THP = trianionic tris-ß-diketonate, and iPr-Pybox = chiral bis(4-isopropyl-2-oxazolinyl)pyridine). X-ray crystallographic analysis revealed that the octanuclear circular helicate possesses square antiprism architecture and consists of four [(R)- or (S)-iPr-Pybox]2LnIII2(THP)2 asymmetric units arranged in a closed ring form. Ligand-to-ligand interactions between the THP and the iPr-Pybox ligands have successfully directed formation of enantiopure, homoconfigurational (Δ,Δ,Δ,Δ,Δ,Δ,Δ,Δ)-R and (Λ,Λ,Λ,Λ,Λ,Λ,Λ,Λ)-S isomers. All of the nonacoordinated LnIII ions are identical and exhibit a distorted capped square antiprism (CSAP) geometry. Upon excitation of the ligand absorption band (λ = 360 nm), the circular helicates display characteristic EuIII (red, 5D0 → 7FJ, J = 0-4) or TbIII (green, 5D4 → 7FJ, J = 6-3) core f-f luminescence. The overall emission quantum yields of the circular EuIII and TbIII helicates are 0.145 and 0.0013, respectively, in chloroform. The EuIII and TbIII complexes exhibit remarkable circularly polarized luminescence (CPL) activity at their magnetic dipole transition with observed luminescence dissymmetry factors |glum| of 1.25 (5D0 → 7F1, λ = 592 nm) and 0.25 (5D4 → 7F5, λ = 541 nm), respectively. Exceptional |glum| values of the circular EuIII helicates highlight the visible intensity difference between left and right circularly polarized emissions of R and S isomers in chloroform and PMMA thin film.

Chirogenesis and Pfeiffer Effect in Optically Inactive EuIII and TbIII Tris(ß-diketonate) Upon Intermolecular Chirality Transfer From Poly- and Monosaccharide Alkyl Esters and α-Pinene: Emerging Circularly Polarized Luminescence (CPL) and Circular Dichroism (CD).

We report emerging circularly polarized luminescence (CPL) at 4f-4f transitions when lanthanide (EuIII and TbIII) tris(ß-diketonate) embedded to cellulose triacetate (CTA), cellulose acetate butyrate (CABu), D-/L-glucose pentamethyl esters ( D-/ L-Glu), and D-/L-arabinose tetramethyl esters ( D-/ L-Ara) are in film states. Herein, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate (fod) and 2,2,6,6-tetramethyl-3,5-heptanedione (dpm) were chosen as the ß-diketonates. The g lum value of Eu(fod)3 in CABu are +0.0671 at 593 nm (5 D 0 → 7 F1) and -0.0059 at 613 nm (5 D 0 → 7 F2), respectively, while those in CTA are +0.0463 and -0.0040 at these transitions, respectively. The g lum value of Tb(fod)3 in CABu are -0.0029 at 490 nm (5 D 4 → 7 F6), +0.0078 at 540 nm (5 D 4 → 7 F5), and -0.0018 at 552 nm (5 D 4 → 7 F5), respectively, while those in CTA are -0.0053, +0.0037, and -0.0059 at these transitions, respectively. D-/ L-Glu and D-/ L-Ara induced weaker g lum values at 4f-4f transitions of Eu(fod)3, Tb(fod)3, and Tb(dpm)3. For comparison, Tb(dpm)3 in α-pinene showed clear CPL characteristics, though Eu(dpm)3 did not. A surplus charge neutralization hypothesis was applied to the origin of attractive intermolecular interactions between the ligands and saccharides. This idea was supported from the concomitant opposite tendency in upfield 19F-NMR and downfield 1H-NMR chemical shifts of Eu(fod)3 and the opposite Mulliken charges between F-C bonds (fod) and H-C bonds (CTA and D-/ L-Glu). An analysis of CPL excitation (CPLE) and CPL spectra suggests that (+)- and (-)-sign CPL signals of EuIII and TbIII at different 4f-4f transitions in the visible region are the same with the (+)-and (-)-sign exhibited by CPLE bands at high energy levels of EuIII and TbIII in the near-UV region.

Self-assembled Tetranuclear EuIII Complexes with D2- and C2h-Symmetrical Square Scaffold.

Three new tetranuclear europium(III) alternating circular helicates, (2-PhRRRR/2-PhSSSS) [(R)- or (S)-Ph-Pybox]4EuIII4(BPP)6, (2-iPrRRRR/2-iPrSSSS) [(R)- or (S)-iPr-Pybox]4EuIII4(BPP)6, and (3-PhRRRR/3-PhSSSS) [(R)- or (S)-Ph-Pybox]4EuIII4(BHP)6, are presented with their structural and chiroptical characterization (BPP and BHP = bis-ß-diketonates; Pybox = chiral bis(oxazolinyl) pyridine ligand). X-ray crystallographic analysis revealed that different extents of interligand-contacting interactions between bis-ß-diketonates and Pybox ligands produce different bis-ß-diketonates arrangements around four EuIII ions and, thus, their specific symmetry in the final tetranuclear complexes. 2-PhRRRR/2-PhSSSS and 3-PhRRRR/3-PhSSSS are recognized as D2-symmetry, while 2-iPrRRRR/2-iPrSSSS self-assemblies possess pseudo C2h-symmetry. Due to different molecular symmetry, 2-PhRRRR/2-PhSSSS and 2-iPrRRRR/2-iPrSSSS crystals display different ligands orientation in their EuIII coordination spheres. The presence of pseudo σh-mirror symmetry in 2-iPrRRRR/2-iPrSSSS promotes a pair of distinguishable EuIII geometries. All the chiral self-assemblies exhibit almost identical photoluminescence emission spectra patterns of f-f transitions in the EuIII core. The EuIII self-assemblies exhibit intense CPL with different observed |glum| values (2-PhRRRR/2-PhSSSS ∼ |0.31|, 2-iPrRRRR/2-iPrSSSS ∼ |0.08|, 3-PhRRRR/3-PhSSSS ∼ |0.31| in chloroform).

Solvation of quantum dots in 1-alkyl-1-methylpyrrolidinium ionic liquids: toward stably luminescent composites.

CdTe nanoparticles capped with a cationic thiolate ligand were stably dispersed in ionic liquids, 1-alkyl-1-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)amides with an alkyl group of n-propyl, butyl and octyl-chain, and in an ionic plastic crystal, 1-ethyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide. Dispersion behavior of CdTe nanoparticles in these ionic media was evaluated, in which the solvation of nanoparticles by the ionic components was particularly interested. The ionic media showed alkyl-chain length-dependent solvation behavior, which was suggested by the thermal analysis of nanocomposites. The longer alkyl-chains led to the greater decrease in the thermal melting enthalpy of ionic media with the introduction of nanoparticles. The ionic liquid with an octyl-chain, which is considered to form a thicker solvation layer, afforded better emission durability of CdTe nanoparticles compared to the ionic liquid with a shorter alkyl chain.